1. Field of the Invention
The present invention relates to a multimode type mobile communication terminal apparatus used in an area where a plurality of systems provide services.
2. Description of the Related Art
For example, North America has an area where an analog system (AMPS: Advanced Mobile Phone System) and a plurality of digital systems (PCS: Personal Communication System and CDMA: Code Division Multiple Access system) provide services. As a mobile communication terminal apparatus used in such an area, a multimode type mobile communication terminal apparatus capable of accessing any of these systems has been developed.
As a control mode for selecting a system, the multimode type mobile communication terminal apparatus is equipped with an automatic system selection mode (to be referred to as an automatic mode hereinafter) and an analog only mode.
In the automatic mode, the mobile communication terminal apparatus sequentially searches control signals transmitted by respective systems from their base stations upon power-on of the mobile communication terminal apparatus. If the mobile communication terminal apparatus detects by this search a control signal which satisfies a predetermined condition, the apparatus acquires the base station which has transmitted the control signal, and shifts to the standby state.
At this time, search priority is set in advance for the digital and analog systems. For example, the digital system is assigned a higher priority than the analog system. In this case, the mobile communication terminal apparatus searches for a control signal transmitted by the base station of a digital system. If the apparatus does not detect by this search any digital system which satisfies a condition, the apparatus then searches for a control signal transmitted by the base station of an analog system. If the apparatus detects a control signal which satisfies the condition, the apparatus acquires the base station of the analog system which has transmitted the control signal, and shifts to the standby state.
In the analog only mode, the mobile communication terminal apparatus searches control signals transmitted by the base stations of a plurality of systems for only a control signal transmitted by an analog system. If the apparatus detects a control signal which satisfies a condition, the apparatus acquires the base station which has transmitted the control signal, and shifts to the standby state.
The power consumption in speech communication is generally higher in the analog system than in the digital system. In the multimode type mobile communication terminal apparatus, the automatic mode has a higher priority than the analog only mode, and a system is selected in the automatic mode in a normal state. Depending on the location of the terminal apparatus, only weak radio waves may be received from the base station of a digital system. Leaving this state to stand unpreferably decreases the connection completion ratio. In this case, the user changes the system selection mode to the analog only mode. This operation changes the system selection mode of the terminal apparatus to the analog only mode, and an analog system is acquired in accordance with the analog only mode. After that, the terminal apparatus can perform stable standby operation between the apparatus and an analog system where the reception field is relatively strong.
The conventional terminal apparatus however suffers the following problems. If the system selection mode of the terminal apparatus is once changed to the analog only mode, this state is held even upon power-off of the terminal apparatus unless the user performs mode change operation again. For example, the user temporarily turns off the terminal apparatus when getting on a train or airplane, and turns on the terminal apparatus after getting off the train or airplane. In this case, the terminal apparatus executes system selection operation in the analog only mode, and as a result, acquires an analog system. If the user keeps using the terminal apparatus in this state without being aware of it, a larger amount of power than in the digital system is consumed. The battery runs out faster than expected, and the terminal apparatus cannot be used.